1. Field of the Invention
The present invention relates to a liquid crystal display device and, more specifically, to a liquid crystal display device which displays three-dimensional videos.
2. Description of the Related Art
Recently, there has been a rapidly increasing demand for a display capable of displaying three-dimensional videos, i.e., so-called 3D videos. A large number of researches and studies on the techniques for displaying the three-dimensional videos have been done from the past, and studies and developments thereof are actively conducted at present as well. Among those, one of the techniques considered as most potential currently is the technique using binocular parallax.
Three-dimensional video display devices using the binocular parallax are almost classified into two types. One is a type which shows different videos for the left and right eyes by using exclusively-used eyeglasses (referred to as “eyeglass type” hereinafter). The other is a type which spatially separates and displays light of different images for the left and right eyes outputted from a three-dimensional video display device without using exclusively-used eyeglasses (referred to as “naked-eye type” hereinafter).
The former eyeglass type is the type that is suited for a case where a plurality of observers view a relatively large screen simultaneously, and it is used in movie theaters, for television sets, and the like. The latter naked-eye type is the type suited for a case where a single observer views a relatively small screen. The naked-eye type is free from the use of the exclusively-used eyeglass and enables the observer to view three-dimensional videos easily, so that it is expected to be applied for displays of mobile terminals, digital still cameras, video cameras, and notebook-type computers.
As an example of the naked-eye type liquid crystal display device capable of displaying three-dimensional videos, there is a structure disclosed in Japanese Unexamined Patent Publication 2006-030512 (Patent Document 1). As shown in FIG. 27, Patent Document 1 discloses the liquid crystal display device in which: 3×3 pixels are disposed in a matrix form in the X-axis direction and the Y-axis direction; and a single pixel 6 is constituted with six sub-pixels 61 (RR, RL, GR, GL, BR, BL). In the liquid crystal display device, two color images constituted with light of R (Red), G (Green), and B (Blue) are shown on the single pixel 6 constituted with the six sub-pixels 61 for the left eye and the right eye of an observer. The sub-pixel RR displays a red image for the right eye, the sub-pixel RL shows a red image for the left eye. Similarly, the sub-pixels GR, GL, BR, and BL show a green image for the right eye, a green image for the left eye, a blue image for the right eye, and a blue image for the left eye, respectively. In FIG. 27, a part of gate lines G1 to G9 and a part of data lines D1 to D6 are illustrated.
As shown in FIG. 28 and FIG. 29, the liquid crystal display device employs the structure in which a lens array sheet 3 having cylindrical lenses 31 with a pitch PL being arranged in array in the X-axis direction is disposed on a liquid crystal panel 2 having a matrix of pixels arranged in the X-axis direction and the Y-axis direction with a pitch PP. Further, as shown in FIG. 29, red light for the right eye emitted from the sub-pixel RR is radiated to a space ZR by the cylindrical lens 31. Similarly, red light for the left eye is radiated to a space ZL by the cylindrical lens 31. When the right eye 9R of the observer is set in the space ZR and the left eye 9L is set in the space ZL, the observer sees only the image for the right eye with the right eye 9R and see only the image for the left eye with the left eye 9L. Thus, the observer can visually recognize the image displayed on the liquid crystal display device as a three-dimensional video. In FIG. 29, light-shielding sections 80 are illustrated between the sub-pixels.
Further, this liquid crystal display device is also capable of displaying two-dimensional videos through displaying same images on the sub-pixels for the right eye and the sub-pixels for the left eye. Considering such current circumstances that the apparatuses for displaying images do not always display three-dimensional videos and that the proportion of displaying the three-dimensional videos is smaller, it is important to be able to display two-dimensional videos in terms of the practical use. Further, for displaying the two-dimensional videos, it is also required to have a wide viewing angle property with which displayed videos are viewed as same even when the liquid crystal display device is observed from any angles of directions.
However, with the liquid crystal display device disclosed in Patent Document 1 described above, there is such an issue that moiré is likely to be visually recognized when two-dimensional videos are displayed. Further, there is no consideration being taken to satisfy the demand for improving the viewing angle property.
Next, the mechanism for generating moiré will be described. A cylindrical lens exhibits no lens effect for the axial direction of the lens but exhibits the lens effect for the direction at an acute angle with respect to the axis. In the case of FIG. 28, the axis direction of the cylindrical lens 31 is the Y-axis direction, and the direction at an acute angle with respect to the axis is the X-axis direction. As shown in FIG. 29, when the liquid crystal panel 2 is disposed in the vicinity of the focal point of the cylindrical lens 31, the light emitted from the liquid crystal panel 2 is projected to the direction tilted with respect to the Z-axis. The angle thereof is determined according to the relation between the vertex of the cylindrical lens 31 and the position of the X-axis of the liquid crystal panel 2. Therefore, in a case where the intensity of the light emitted from the liquid crystal panel 2 varies depending on the position of the X-axis, the extent of the light in terms of the intensity varies depending on the angles at which the light is emitted. That is, in a case where the light-shielding section 80 that does not radiate the light exists on the liquid crystal panel 2 and the light-shielding section 80 is extended in the Y-axis direction, there is no light existing in the direction of a certain angle radiated from cylindrical lens 31, which is visually recognized as black. This is the mechanism for generating the moiré. Completely the same phenomenon occurs even in a case where a parallax barrier is used instead of the cylindrical lens 31.
The light-shielding section described above is located between two sub-pixels disposed neighboring to each other in the X-axis direction of the liquid crystal panel. Thus, the region visually recognized as black is located between the region where the left-eye image is projected and the region where the right-eye image is projected. When the liquid crystal display device is displaying a three-dimensional video, the observer moves the face so that the left eye and the right eye come to be at appropriate positions, respectively, in order to be able to visually recognize the image as the three-dimensional video. However, when the liquid crystal display device is displaying a two-dimensional video, the observer cannot sense the appropriate positions. Thus, there may be cases where the eyes are located at the region visually recognized as black depending on the position of the face, which may deteriorate the display quality greatly.
As a technique for suppressing the moiré, there is a technique disclosed in Japanese Unexamined Patent Publication Hei 10-186294 (Patent Document 2). FIG. 30 shows sub-pixels 61 of the liquid crystal display device capable of displaying three-dimensional videos disclosed in Patent Document 2. As described above, the moiré is generated because the intensity of the light emitted from the liquid crystal panel changes depending on the position of the X-axis. The intensity of the light emitted from the liquid crystal panel according to the position of the X-axis is equivalent to the ratio between the aperture section and the light-shielding section when the aperture section of the liquid crystal panel is cut in the Y-axis direction at the position of the X-axis. Thus, in order to overcome the moiré, the ratio between the aperture section and the light-shielding section may be set as constant regardless of the positions in the X-axis direction. Regarding the sub-pixels 61 disclosed in Patent Document 2, the light-shielding section extending in the Y-axis direction is tilted at an angle θ with respect to the X-axis. Provided that the width of the oblique light-shielding section is e, the width d of the light-shielding section in the Y-axis direction can be expressed with a following expression.d=e/cos θ  [1]
The width of the aperture section in the part where the oblique light-shielding section exists is the sum of the widths b and c. When sides Et and Eb which define the aperture section are in parallel, the sum of the widths b and c becomes constant regardless of the positions in the X-axis direction. In the meantime, in the region where there is no oblique light-shielding section, the width a of the aperture section becomes constant regardless of the position in the X-axis direction and becomes equivalent to the sum of the widths b and c by setting the width f to be equivalent to the width d when the sides Et′ and Eb which define the aperture section are in parallel. Note that sides E1, E1′, and Er are parallel to each other.
Further, as another structure for suppressing the moiré disclosed in Patent Document 2, there is a pixel layout shown in FIG. 31. In this layout, a pixel displaying a same signal is divided into two sub-pixels SP1 and SP2, and a data line 62 is disposed between those. There is a limit for set for reducing the width of the data line 62 in terms of the manufacture process, so that it is difficult to reduce the width e in the case of FIG. 30. This causes an issue of deteriorating the numerical aperture. However, in the case of FIG. 31, it is possible to set an angle θ2 to be small for the Y-axis of the light-shielding section in the part where the data line 62 is disposed with respect to an angle θ1 for the Y-axis of the light-shielding section in the boundary part of the neighboring pixels. Therefore, it is possible with this to reduce the deterioration in the numerical aperture.
As the techniques for suppressing the moiré, there are various methods (Japanese Unexamined Patent Publication 2008-092361 (Patent Document 3) and Japanese Unexamined Patent Publication 2008-249887 (Patent Document 4)) other than the technique disclosed in Patent Document 2.
As a technique for acquiring a wide viewing angle property with the liquid crystal display device, there is a technique using an IPS (In-Plane Switching) mode. The IPS mode controls the director direction of liquid crystal molecules with an electric field in parallel to the surface of a substrate which constitutes the liquid crystal display device. The directors of the liquid crystal molecules move in parallel to the electric field and hardly move in the normal direction of the substrate surface. Therefore, this mode exhibits such a characteristic that the viewing angle property thereof is essentially better than other modes.
Normally, in the IPS-mode liquid crystal display device, a common electrode that is in common to all the sub-pixels and pixel electrodes of each of the sub-pixels are arranged on a same substrate in a comb-like form, and liquid crystal molecules are controlled with the electric fields generated between those electrodes. A specific voltage is applied to the common electrode, and signal voltages according to the videos to be displayed are applied to the pixel electrodes of the individual sub-pixels. In order to write the signal voltages, a TFT (Thin Film Transistor) in which the source electrode is connected to the data line, the drain electrode is connected to the pixel electrode, and the gate electrode is connected to the gate line is disposed in each sub-pixel. Through supplying a signal voltage to the data line while the voltage of the gate line is set as a voltage with which the TFT is in a conductive state, the signal voltage is written to the pixel electrode.
As described, with the IPS mode, the liquid crystal molecules are controlled with the electric field generated between the common electrode and the pixel electrodes. Thus, when the electric field between the common electrode and the pixel electrodes is influenced by the electric field from the gate line or the data line, faults such as crosstalk and the like occur. Particularly, the potential of the data line fluctuates according to the videos to be displayed, so that it is necessary to shield the electric field radiated from the data line at least in order to prevent the faults such as the crosstalk and the like. Regarding the shielding technique, there is a technique disclosed in Japanese Unexamined Patent Publication 2002-323706 (Patent Document 5).
FIG. 32 shows a pixel layout of the IPS mode disclosed in Patent Document 5. In each pixel, a pixel electrode 70 and a common electrode 71 arranged in a comb-like form, a TFT 64, a data line 62, a gate line 63, a storage capacitance line 67, and a common potential wiring 68 are provided. FIG. 33 is a sectional view taken along a line A-A′ of FIG. 32. As can be seen from FIG. 33, on the TFT substrate 4, the common electrode 71 having a wider width than that of the data line 62 covers over the data line 62 via an interlayer film 46. By employing such structure, the electric field radiated from the data line 62 is shielded so as not to influence the electric field between the pixel electrode 70 and the common electrode 71. Therefore, the crosstalk can be suppressed greatly.
However, when the pixel layout (FIG. 30, FIG. 31) which reduces the moiré disclosed in Patent Document 2 and the pixel structure (FIG. 32, FIG. 33) of the IPS mode disclosed in Patent Document 5 are applied to the liquid crystal display device (FIG. 27, FIG. 28, FIG. 29) which displays three-dimensional videos disclosed in Patent Document 1, there is generated such a new issue that the numerical aperture is deteriorated greatly. The reason thereof will be described in a simple manner.
The technique for reducing the moiré disclosed in Patent Document 2 (FIG. 30) is a technique with which, provided that the light-shielding section that does not radiate the light located between the sub-pixels neighboring to each other in the X-axis direction is disposed obliquely with respect to the axis (Y-axis) of the cylindrical lens and that the length of the light-shielding section in the Y-axis direction is d, the length in the Y-axis direction of the aperture section at a place (side Et′) where the light-shielding section is not disposed at the position of the aperture section in the X-axis direction is reduced for the length of d. This d is determined according to the space e between the sub-pixels neighboring to each other in the X-axis direction and the tilt θ between the light-shielding section and the X-axis, and it is necessary to reduce the values of e and θ in order to reduce the value of d.
When the pixel structure (FIG. 32 and FIG. 33) disclosed in Patent Document 5 is applied for the purpose of widening the viewing angles of the liquid crystal display device, it is necessary to cover the data line with the common electrode that has the wider width than that of the data line in order to shield the electric field from the data line located at the position of e. The liquid crystal molecules are controlled with the electric field between the common electrode and the pixel electrode in the IPS mode, so that an electric field constituted with a component in parallel to the substrate surface is hardly generated on the common electrode. Thus, the liquid crystal molecules hardly move. This means that the common electrode functions as the light-shielding section and that the length corresponding to d becomes long. In the meantime, when θ is set to be small, the length of the part where the aperture sections of the neighboring sub-pixels overlap with each other in the X-axis direction becomes long. The light emitted from the overlapping region reaches the eyes of the observer by being mixed with the light emitted from the neighboring sub-pixels, so that the observer simultaneously views the image for the left eye and the image for the right eye with one of the eyes. This may sometimes be called 3D crosstalk, and it becomes difficult for the observer to visually recognize an image as a three-dimensional video when the mixing ratio of the light becomes high. That is, θ cannot be set small for securing the numerical aperture, so that the numerical aperture is deteriorated greatly.
Therefore, it is investigated to make θ small by applying the technique shown in FIG. 31, which is disclosed in Patent Document 2. With the IPS mode, the director direction of the liquid crystal molecules is controlled with the electric field that is in parallel to the substrate surface generated between the pixel electrode and the common electrode arranged in a comb-like form to display videos. Thus, the liquid crystal molecules on the pixel electrode and the common electrode hardly move. Therefore, even when the pixel electrode and the common electrode are formed with a transparent conductive film such as ITO (Indium Tin Oxide) or the like, the pixel electrode and the common electrode turn out as the light-shielding sections that do not transmit the light. That is, there are a great number of light-shielding sections formed with the pixel electrode and the common electrode in the sub-pixels SP1 and SP2 shown in FIG. 31, so that the condition for suppressing the moiré is not satisfied. Therefore, while the deterioration in the numerical aperture can be reduced, the moiré cannot be suppressed.
As described above, when the structure (FIG. 32 and FIG. 33) of patent Document 5 with which the width e of the light-shielding section between the neighboring sub-pixels becomes large is employed, either the numerical aperture is deteriorated greatly or generation of the moiré cannot be suppressed.
It is therefore an exemplary object of the present invention to provide a liquid crystal display device having a wide viewing angle property capable of displaying three-dimensional videos, with which: generation of the moiré can be suppressed; only little crosstalk is generated; and a high numerical aperture can be achieved.